The present invention relates to highway guardrail systems having a guardrail mounted on posts, and more particularly, to guardrail end terminals having at least two posts with a strut extending therebetween and the end terminals designed to meet applicable federal and state safety standards including but not limited to crash worthiness requirements.
Along most highways there are hazards which present substantial danger to drivers and passengers of vehicles if the vehicles leave the highway. To prevent accidents from a vehicle leaving a highway, guardrail systems are often provided along the side of the highway. Experience has shown that guardrails should be installed such that the end of a guardrail facing oncoming traffic does not present another hazard more dangerous than the original hazard requiring installation of the associated guardrail systems. Early guardrail systems often had no protection at the end facing oncoming traffic. Sometimes impacting vehicles became impaled on the end of the guardrail causing extensive damage to the vehicle and severe injury to the drivers and/or passengers. In some reported cases, the guardrail penetrated directly into the passenger""s compartment of the vehicle fatally injuring the driver and passengers.
Various highway guardrail systems and guardrail end terminals have been developed to minimize the consequences resulting from a head-on impact between a vehicle and the extreme end of the associated guardrail. One example of such end terminals includes tapering the ends of the associated guardrail into the ground to eliminate potential impact with the extreme end of the guardrail. Other types of end terminals include breakaway cable terminals (BCT), vehicle attenuating terminals (VAT), the SENTRE end terminal, and breakaway end terminals (BET).
It is desirable for an end terminal assembly installed at one end of a guardrail facing oncoming traffic to attenuate any head-on impact with the end of the guardrail and to provide an effective anchor to redirect a vehicle back onto the associated roadway after a rail face impact with the guardrail downstream from the end terminal assembly. Examples of such end terminals are shown in U.S. Pat. No. 4,928,928 entitled Guardrail Extruder Terminal, and U.S. Pat. No. 5,078,366 entitled Guardrail Extruder Terminal.
A SENTRE end terminal often includes a series of breakaway steel guardrail support posts and frangible plastic containers filled with sandbags. An impacting vehicle is decelerated as the guardrail support posts release or shear and the plastic containers and sandbags are compacted. A cable is often included to guide an impacting vehicle away from the associated guardrail.
Wooden breakaway support posts are frequently used to releasably anchor guardrail end terminals and portions of the associated guardrail. Such wooden breakaway support posts, when properly installed, generally perform satisfactorily to minimize damage to an impacting vehicle during either a rail face impact or a head-on impact. However, impact of a vehicle with a wooden breakaway support post may often result in substantial damage to the adjacent soil. Removing portions of a broken wooden post from the soil is often both time consuming and further damages the soil. Therefore, wooden breakaway support posts are often installed in hollow metal tubes, sometimes referred to as foundation sleeves, and/or concrete foundations. For some applications, one or more soil plates may be attached to each hollow tube or foundation sleeve to further improve breakaway characteristics of the associated wooden post. Struts are particularly helpful in maintaining the hollow tubes or foundation sleeves securely positioned adjacent to the roadway during vehicle impact with the associated guardrail. Also, various types of struts have between disposed between and coupled with the associated wooden posts to improve the breakaway characteristics.
From the foregoing, it may be appreciated that a need exists to provide improved support for breakaway support posts associated with guardrail end terminals. According to one embodiment of the present invention, this need is met by an angle strut extending between and coupled with a first hollow tube and a second hollow tube, both of which may be inserted into the soil adjacent to a roadway. Respective support posts may be inserted into the hollow tubes and coupled with the angle strut. For some applications, more than one angle strut may be installed between a first support post and a second support post.
Each support post will generally resist a rail face impact with the guardrail (strong direction). An impact with one end of the attached guardrail (weak direction) will tend to rotate and/or break the support posts proximate the associated hollow tube. Each support post preferably exhibits a high mechanical strength in the strong direction and lower mechanical strength in the weak direction. Generally, the strong direction and the weak direction for each support post are approximately perpendicular relative to each other. Placing an angle strut between the first support post and the second support post of a guardrail end terminal in accordance with teachings of the present invention provides desired support for an associated cable anchor assembly. The angle strut also provides additional support to ensure failure of the associated support posts at a desired location immediately above the respective hollow tubes to help maintain the hollow tubes securely positioned adjacent to the roadway. As a result overall cost of maintenance and repair of an associated guardrail end terminal assembly following a crash event may be substantially reduced.
The present invention provides an angle strut which substantially reduces manufacturing and assembly costs for an associated guardrail end terminal assembly, while at the same time allowing the guardrail end terminal assembly to effectively anchor the guardrail during a downstream side-face impact and to function satisfactorily during a head-on impact with one end of the guardrail without excessive damage to the impacting vehicle. An angle strut incorporating teachings of the present invention may be disposed between a first support post and a second support post having either right or left lateral offset relative to the guardrail.
An end terminal assembly is often provided at one end of a guardrail facing oncoming traffic to substantially enhance the safety of a vehicle impacting at or near the end of the guardrail. An end terminal assembly incorporating teachings of the present invention may be used with a guardrail mounted on a plurality of breakaway support posts made from wood or other suitable materials. A first post is preferably provided adjacent to an extreme end of the guardrail. A second post may be spaced longitudinally from the first post with an angle strut extending therebetween. For some applications the first and second posts may be aligned substantially parallel with each other and the guardrail. For other applications the second post may be spaced longitudinally from the first post and offset laterally from the guardrail. The end terminal assembly may include a kinetic energy absorbing assembly such as an extruder terminal that dissipates energy from an impacting vehicle by squeezing a W-beam guardrail into a relatively flat plate and bending the flattened guardrail in an arc directed away from the impacting vehicle. Other types of kinetic energy absorbing assemblies may be satisfactorily used with an end terminal assembly having at least one angle strut incorporating teachings of the present invention. Alternatively, an angle strut incorporating teachings of the present invention may be satisfactorily used with an end terminal assembly which does not include a kinetic energy absorbing assembly.
Technical advantages of the present invention include providing an end terminal assembly for a highway guardrail system which is less expensive to manufacture than prior designs and which is easier to install. An angle strut incorporating teachings of the present invention may be fabricated from a single piece of commercially available angle or other suitable types of construction and structural materials. Prior to the present invention, separate right hand struts and left hand struts were sometimes required depending upon the direction of the lateral offset of the second support post from the associated guardrail. An angle strut incorporating teachings of the present invention may be used with either a right offset or a left offset.